This invention relates to gas-insulated systems, and more specifically relates to a novel arrangement for determining the location of an insulator which may have been subjected to flashover damage during an internal insulation failure.
Gas-insulated systems are well known and commonly consist of a high voltage central conductor which is contained within an outer elongated grounded housing which is filled with a high dielectric gas such as sulfur hexafluoride under positive pressure. Support insulators are positioned within the housing and are spaced along the length of the conductor to support the central conductor within its grounded outer housing.
Although it occurs infrequently, it is possible that the internal insulation system will fail. Once there is a failure, it is necessary to determine its exact location along the conductor so that the involved conductors and insulators can be repaired. Since all flashover damage is likely to be completely contained within the grounded metal housing, there is normally no outward indication of the location of the fault. Moreover, from relay and circuit breaker records which will be available at the electrical power station, it will be known only that a fault has occurred in a particular zone. Within this zone and on the faulted phase there may be a very large number of support insulators spaced, for example, about 25 feet along the length of the conductor and may also include a number of separate gas sections, disconnect switches, breaker terminals, and possibly line terminals. Thus, the location of the fault can be an extremely difficult, time-consuming and expensive task which is necessary before the repair can be carried out. Moreover, the repair becomes inordinately expensive when the repair procedure requires the opening of the gas-insulated sections for inspection only to determine whether the fault has occurred in a particular location.
The point of failure is most likely to be one of the support insulators since a power fault, if not initiated directly at an insulator, is likely to motor rapidly to an insulator.
In the past, numerous procedures have been used to try to locate the area of the fault after the fault has occurred. This has included energizing the line and then having personnel listen to the line at the various locations for the noise which would be associated with corona discharge or the like in the faulted region. This method is not too satisfactory and, moreover, when a line which has faulted is reenergized, it sometimes will give no indication of the existence of a damaged region and the damaged region may withstand system voltage for a short time before failing completely. Another system has been described in a paper F 79228-8, entitled "Dynamic Behavior of Metal Enclosures for Gas-Insulated Substations During Ground Faults and Their Immediate Location by Mechanical Means" by Tominaga et al. approved by the IEEE Substations Committee of the IEEE Power Engineering Society and to be presented at the IEEE PES Winter Meeting in New York Feb. 4-9, 1979. This paper discloses the use of mechanical devices for locating mechanical abnormalities along the length of a gas-insulated system.
The present invention provides a novel, simple and inexpensive sensor which can be located adjacent the location of every support insulator or adjacent selected support insulators along the length of a gas-insulated system. The sensors are operated in response to the presence of a non-zero magnetic field exterior to the grounded conductor housing of the system. This field will vary depending upon the location of a fault within the system and the location of ground connections to the system and the location of the sources of the power current infeed. However, by comparing the operation of the various sensors located along the line, one can immediately determine the exact location of a fault by determining those points along the grounded conductive sheath at which there appeared an instantaneous non-zero magnetic field.
In carrying out the present invention, two pairs of "exploring coils" are provided adjacent each insulator location and are associated with a conventional commercially available electromagnetic target assembly which consists of a permanent magnet and coil assembly. These assemblies may be located at any desired location in the gas-insulated system such as on the gas bus sections. The operation or non-operation of the indicators in the sensors would then be examined following the internal fault to provide a positive and visual indication of the position of the fault to the nearest insulator within the system or to a particular gas bus section between the insulators. Suitable reset means are provided to reset the targets after a fault condition has occurred.